Harsh drilling conditions can exceed the capabilities of traditional drill string connections. As the petroleum industry moves toward more severe drilling applications - deepwater, extended reach, high-angle, short-radius and ultra-deep wells - new drill string connection designs are required to safely and efficiently achieve the drilling objectives of these projects. This paper describes three new rotary shoulder connections that provide significant operational advantages for extreme drilling applications.
An advanced, high-performance tool joint design provides approximately 70% more working torque capacity than standard API connections. This new design is a second-generation, double-shoulder connection that is optimized for each drill pipe size. The connection's increased torsional strength allows for the use of a streamlined tool joint configuration. The connections can be configured with a smaller OD and larger ID compared to standard API connections without sacrificing torsional capacity.
A second version of this connection incorporates a radial metal-to-metal internal pressure seal. This connection provides high torsional strength combined with gas-tight pressure sealing capability. Drill strings with the gas-tight connection can be used for drill stem testing (DST) operations, underbalanced drilling and high-pressure workover and completion operations. This eliminates the need for a separate work string saving time, money, rig space and set back capacity. This is a significant advantage in offshore operations where rig space and set back capacity are at a premium.
A third development discussed in the paper is a new thread form that provides increased durability and improved fatigue life compared to standard API connections. This thread form has been successfully used on drill pipe pins and drill collar boxes.
This paper discusses the engineering philosophy behind each of these new designs and details results of physical testing. Applications where the connections have been used are also presented.
Design Configuration and Capabilities
The eXtreme™ Torque (XT™) is a second-generation double-shoulder connection (see Figure 1). The XT design evolved from the design of the HI TORQUE (HT™) connection.
Figure 2 depicts the make-up characteristics of XT and HT. Both connections spin up freely from the stab-in to hand-tight position. In the hand-tight position the primary external shoulder makes contact. As the connection is made-up from the hand-tight to power-tight position the box counterbore compresses and the pin base elongates elastically and the secondary torque stop engages. The secondary torque shoulder provides the increased torsional capacity compared to a standard API rotary shoulder connection.
The external (primary) shoulder is the pressure seal for the connection just as on an API connection. Since the secondary shoulder functions solely as a torque stop and not a pressure seal, minor damage to the secondary shoulder can be tolerated without adversely effecting connection performance provided there is no protruding metal that will impede contact between the shoulder surfaces. Any protruding metal on the secondary shoulder must be removed with a file or abrasive paper. Use of thread protectors when the pipe is racked back in the derrick is not required or recommended.